an ice cube at an unknown temperature is added to $25.0$ g of liquid $\ce{h2o}$ at $40.0$ $^\circ\text{c}$. the final temperature of the $29.3$ g equilibrated mixture is $21.5$ $^\circ\text{c}$. what was the original temperature of the ice cube? \begin{align*} c {p,\textrm{water}}